Macrophages have a critical role in inflammatory and immune responses through their ability to recognize and engulf apoptotic cells (Savill et al. (2002) Nature Rev. Immunol. 2:965-975, herein incorporated by reference in its entirety). It is widely believed that macrophage involvement in programmed cell death occurs after the apoptotic event in response to membrane-tethered or soluble “eat-me” signals from dead and dying cells. However, in some circumstances phagocytes actively induce programmed cell death. In mice, macrophages are required for the programmed regression of temporary capillary networks within the developing eye (Lang, R. A. & Bishop, M. J. (1993) Cell 74:453-462 and Diez-Roux, G. & Lang, R. A. (1997) Development 124:3633-3638, herein incorporated by reference in their entirety). The mechanisms governing macrophage involvement in programmed cell death have not been clarified.
The Wingless (Wnt) signaling pathway has a crucial function in developmental cell fate decisions, and when aberrantly activated, in the development of cancer (Bienz, M & Clevers, H. (2000) Cell 103:311-30). In vertebrates, the canonical Wnt response requires a receptor complex comprising the co-receptor Lrp5 or Lrp6 and a multi-transmembrane pass receptor of the frizzled family. When activated by a Wnt ligand, this complex initiates a cascade of events that culminates in stabilization of β-catenin, its association with Lef/Tcf family of transcription factors and the regulation of target genes including some that stimulate cell cycle entry (see Nusse (1999) Trends Genet 15:1-3; Bienz & Clevers (2000) Cell 103:311-320; He et al. (2004) Development 131:1663-1677; Perrimon, N. (1996) Cell 86:513-516; Behrens et al. (1996) Nature 382:638-642, herein incorporated by reference in their entirety).
The Wnt gene family includes at least ten genes that encode structurally related secreted glycoproteins. Members of the Wnt family are reported to be regulators of mammary cell growth and differentiation. For example, dysregulation of Wnt signaling has been reported to cause developmental defects and to be implicated in the genesis of several human cancers. Overexpression of Wnt-7b proteins can result in cellular transformation of C57MG cells. Higher Wnt7b expression levels have also been reported in superficial bladder cancer cells as compared to invasive bladder cancer cells. These results suggest that the Wnt7b polypeptide is involved in the early events of bladder tumorigenesis (U.S. Pat. No. 6,653,448 B1, herein incorporated by reference in its entirety).
Angiopoietins are a family of vascular growth factors that collaborate with members of the vascular endothelial growth factor family to regulate vascular and lymphatic vessel growth, acting via the endothelial receptor tyrosine kinase Tie 2. Although angiopoietin-1 seems to be an obligate activator of the Tie2 receptor, angiopoietin-2 (Ang2) seems to have context specific effects, activating this receptor on some cells while blocking Tie2 activation on other cells or under other conditions. Ang2 is a context-dependent agonist/antagonist of Tie2 and displays a similar multimerization state to angiopoietin-1. See Davis et al. (2003) Nature Structural Biology 10:38-44, herein incorporated by reference in its entirety.
Thus, a mechanistic assessment of Wnt7b and Ang2's in vivo role is desirable. It is of importance to develop methods of modulating vascular endothelial cell vessel formation. It is of further importance to develop methods of modulating Wnt7b expression.